Sensitivity depends on the demand of the ride. I have no doubt you can jump on just about any bike and feel fine on a morning ride, but when you get into a 100km, a 160km, a 200km, a 300km, and beyond, etc; at a certain point, believe me, you're going to get "sensitive".
If you can currently do a 200km ride and feel fine, then a bike fit may allow you to extend that to 250km without any additional discomfort. That's from a postural perspective of course. Your endurance is still your own responsibility.
And if you never do more than a century, a proper fit can still help you enjoy the ride more.
The question I'd have, though, would be how many riders require something outside of what's normally supplied? I had a pro bike fit about 25 years ago, which worked so well I have carefully replicated it on all my bikes. When I bought my Canyon Endurace in 2020, I was able to get it within a few mm of that fit with nothing but the parts it came with. I wonder what percentage of cyclists that's true for? If it's the vast majority of cyclists, then there's a lot less incentive/need for either non-proprietary parts, or multiple sizes of proprietary parts for fitting new bikes.